An electrophotographic image forming apparatus forms an image by electrophotography which applies a transfer current to a recording medium, such as a sheet, to attach a recording material to the recording medium. In this type of image forming apparatus, the image formed on the recording medium is thermally fixed. For example, if the recording material is toner, the toner is fused and then fixed onto the recording medium thermally so as to make the image stable.
Further, in this type of image forming apparatus, while an image is thermally fixed to the recording medium, water is evaporated from the recording medium, so that the recording medium is dried. As a result, the heat capacity of the recording medium becomes lower. If the heat capacity of the recording medium is excessively small, a large amount of toner is fused and fixed when an image is formed on a second surface in a double-side printing operation. Accordingly, in order to prevent a large amount of toner from being fused and fixed, a related-art image forming apparatus is provided with a fan for blowing cooling air to a recording medium having an image fixed thereon when humidity is equal to or less than a predetermined value.
The drying of the recording medium further affects an electric resistance value of the recording medium. If a transfer current applied to the recording medium is used to form an image by electrophotography, the electric resistance value of the recording medium greatly affects the formation of an image. Therefore, if the electric resistance value of the recording medium is increased by the evaporation of water, it may be preferable to blow cooling air in order to prevent the recording medium from being dried, as described above.
However, the heat capacity of a recording medium is not necessarily in one-to-one correspondence with the electric resistance value of the recording medium. For example, when the humidity is high and the temperature is low, the recording medium has a large electric resistance value. In this situation, if an image is formed on a second surface without blowing cooling air, the electric resistance value of the recording medium is further increased by the thermal fixation of the image on a first surface, so that it is difficult to form a high-quality image on the second surface.